1. Field of the Invention
The present invention relates to a control device of an internal combustion engine using a fuel having different fuel properties, particularly, a fuel having different alcohol mixing ratios.
2. Background Art
As is described, for example, in JP-2004-285972, a control device of an internal combustion engine of this type in the related art generally permits a concentration estimation in a fuel in a case where an air-fuel ratio correction amount to correct a fuel injection amount is outside a predetermined range even when an alcohol concentration estimation in the fuel is prohibited according to an operating state. According to the device in the related art, in a case where an air-fuel ratio correction amount is outside the predetermined range, a concentration estimation in the fuel is permitted. Hence, by using an estimated concentration estimate value, it becomes possible to prevent deterioration of the running performance and the emission performance caused by an insufficient correction amount.
The device in the related art determines a change of alcohol concentration and permits a concentration estimation in a case where the air-fuel ratio correction amount is outside the predetermined range. However, in a case where a change of the air-fuel ratio correction amount resulting from a change of the alcohol concentration is reflected on another correction amount using the air-fuel ratio correction amount, for example, a purge air concentration correction value, a change of the air-fuel ratio correction amount itself is reduced. This makes it impossible to determine a change of the alcohol concentration. It is therefore anticipated that an estimation of the alcohol concentration is no longer performed. In addition, because the purge concentration correction value takes a wrong value, suitable control is not performed when such a value is kept used.
In particular, in the case of a type that suitably estimates the purge air concentration and updates the purge air concentration correction value from a purge ratio, which is a ratio of a purge amount with respect to an intake air amount, and the purge air concentration when the purge amount has changed, in addition to an erroneous estimation of the purge air concentration due to influences of a change of the alcohol concentration, there is a possibility that a change direction of the alcohol concentration is also wrong.
In a case where the alcohol concentration changes to a low concentration side, the air-fuel ratio changes to a rich side. A feedback correction value therefore takes a value such that corrects the air-fuel ratio to a lean side. The purge air concentration is thus erroneously estimated that it has changed to a high concentration side. When the purge ratio increases in this state, the purge air concentration correction value is updated on the basis of the value erroneously estimated to be on the high concentration side. The purge air concentration correction value therefore takes a value such that corrects the air-fuel ratio further to the lean side.
Consequently, the feedback correction value conversely corrects the air-fuel ratio to the rich side. When a change of the alcohol concentration is determined in this instance, it is erroneously determined that the alcohol concentration has changed to the high concentration side because the feedback correction value takes a value that corrects the air-fuel ratio to the rich side.